Dear Previdi,
SRH may carry Adj Segment and Special segments (128 IPv6 prefixes) along with
Node Segments.
Ex: Consider below Topology
/ B ------ C------- D\
/ Fadj| | \
X --------A | | H----- Y
\ | | /
\ E ---- F ----- G /
At Node X At Node A,
At node C, while forwarding to F (C need to decrement segments to twice,
one for Fadj and other for F)
IPv6 Hdr Ipv6 Hdr
IPv6 Hdr
DA= Y SA=X DA= C SA=X
DA= F SA=X
SRHdr (segment left 4)
SRHdr (segment left 2)
Y,H,F,Fadj,C
Y,H,F,Fadj,C
While processing this type of SRH, I feel existing algorithm may be required to
modify to add recursive look up to process Adj Segment/Special segment as
below. (Based on above example)
Existing algorithm: (As per section 4.3),
1. IF DA = myself (segment endpoint)
2. IF Segments Left > 0 THEN
decrement Segments Left
update DA with Segment List[Segments Left]
3. ELSE continue IPv6 processing of the packet
End of processing.
4. Forward the packet out
Proposed Modification:
1. IF DA = myself (segment endpoint)
2. IF Segments Left > 0 THEN
decrement Segments Left
do
IF Segment List[Segments Left]= Adj-Segment/Special Segment
originated by myself
Trigger the action as per Segment (Ex: if it is Adj
Segment, identify interface to forward, if segment is for the service, trigger
for service)
Decrement Segments Left
ELSE
Update DA with Segment List[Segments Left]
break;
while (Segments Left > 0)
3. ELSE continue IPv6 processing of the packet
End of processing.
4. Forward the packet out
If SRH is having combination of Node and Adj SID then recursive look up to be 2
times maximum at each IPv6 SR supported nodes
If Service Segments are added to SRH, then may be multiple recursive look ups,
since it may require to handle multiple services by same node.
Please check and let me know your opinion.
Thanks & Regards,
Veerendranath
-----Original Message-----
From: Stefano Previdi (sprevidi) [mailto:[email protected]]
Sent: 10 February 2017 15:02
To: Veerendranatha Reddy Vallem <[email protected]>
Cc: [email protected];
[email protected];
[email protected]; [email protected]
Subject: Re: [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH
Hi Veerendranath,
yes, an SR-IPv6 SID is a 128-bit IPv6 addresses.
The semantic associated to the SID is given by the control plane. We have
already documented the signaling of the SIDs in ISIS, OSPF and BGP. Currently
we have defined Node-SIDs (representing a node) and Adjacency-SIDs (instruction
to forward out to the interface the SID is allocated to).
In the IPv6 dataplane a SID being an IPv6 address, it makes the SID a global
IPv6 address (even in the case of Adj-SIDs). This of course is orthogonal to
the control plane that may or may not advertise such address.
I.e., you may have an Adj-SID as a global IPv6 address that it is not
advertised by any routing protocol in the network (which implies of course that
the packet will have to first reach the node using a node-SID).
The use of LL addresses as SID has not been contemplated for the simple reason
that a router may well allocated the same address to all links so it is not a
reliable mechanism for forwarding. This will be fixed in the next revision of
the ospfv3 draft (isis draft is ok).
s.
> On Feb 10, 2017, at 7:37 AM, Veerendranatha Reddy Vallem
> <[email protected]> wrote:
>
> Dear Previdi,
> Thanks for your reply.
>
> As per first version of draft, Adj-SID is also IPv6 prefix.
>
> 4.2.2. Adjacency-SID
>
> The Adjacency-SID identifies a given interface. In the SR
> architecture a node may advertise one or more Adj-SIDs allocated to a
> given interface so to force the forwarding of the packet (when
> received with that particular Adj-SID) into the interface, regardless
> the routing entry for the packet destination. The same is defined
> for SR-IPv6: a node may advertise a given IPv6 prefix which is
> associated to the SR semantic of "send out the packet to the
> interface this prefix is allocated to". Here also, the SID is in
> fact the IPv6 prefix.
>
> As per my understanding "segment list in SRH is global IPv6 prefixes, If we
> need to include Adj SID to segment list then Adj-SID is also global IPv6
> prefix".
> Please correct me if my understanding is wrong.
>
> Thanks and Regards,
> Veerendranath
>
>
>
>
> -----Original Message-----
> From: Stefano Previdi (sprevidi) [mailto:[email protected]]
> Sent: 09 February 2017 22:41
> To: Veerendranatha Reddy Vallem <[email protected]>
> Cc: [email protected];
> [email protected];
> [email protected]; [email protected]
> Subject: Re: [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH
>
> Hi,
>
> the first version of the draft (draft-previdi-6man-segment-routing-header)
> had a description of Node-SID and Adj-SID. Later, in order to simplify the
> document, we removed the descriptions and focused the document into the SRH
> format.
>
> I think it will be helpful to re-introduce a section on the two main SID
> types (Node, Adjacency). I’m working on an update for the next version.
>
> Thanks.
> s.
>
>
>
>
>
>> On Feb 9, 2017, at 5:02 PM, Veerendranatha Reddy Vallem
>> <[email protected]> wrote:
>>
>> Dear Authors,
>>
>> I am requesting your clarification regarding usage of Adj-SID in SRH header
>
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